فصلنامه زیست شناسی گیاهی ایران
سال چهاردهم شماره 2 (پیاپی 52، تابستان 1401)

Plant growth and yield enhancement can be evoked in crops by the exploitation of beneficial microorganisms and the optimal provision of plant nutrients. The effect of inoculation with Serendipita indica and the application of zinc and phosphorus on the growth and yield of strawberries in the aeroponic system was the goal of the present experiment. The study was conducted in a completely randomized design with different levels of inoculation with endophytic fungus S. indica (non-inoculated and inoculated with fungus mycelium) as the first factor and different levels of fertilizer application (0.8 gr zinc sulfate, 1.2 gr monopotassium phosphate, combined zinc-phosphorus and control) as the second factors with three replications. The results showed that the main effects of fertilizer and fungus treatment as well as their interaction effect were significant in all traits except for total protein content. The results also showed that fungus inoculation and zinc and phosphorus application increased traits such as flower and fruit number, shoot and root biomass, chlorophyll, total soluble sugars, protein content, and antioxidant enzymes. In sum, it can be concluded that the effect of phosphorus and zinc fertilizer treatments along with the endophytic fungus S. indica has improved the physiological traits and yield of strawberries. On the other hand, the effects of the simultaneous application of fertilizer and fungus inoculation are more positive than the single application of fertilizer and fungus. Therefore, the optimal application of important elements such as phosphorus and zinc along with the exploration of endophytic symbiotic fungi can be considered a suitable strategy to increase the growth and yield of strawberries.

Today, water shortage is considered one of the main environmental challenges for plants, leading to metabolic and physiological disorders. It has attracted the attention of researchers in recent years. Salicylic acid (SA) and silicon (Si) are considered two drought stress modifiers in plants. To evaluate the drought stress on the physiological and anatomical index of Scrophularia striata for introduction in dry areas during 2020-2021, the present study was conducted as a factorial experiment based on a completely randomized design (CRD) with three replications at the University of Ilam. In this study, drought stress at two levels (50 and 100% of field capacity), SA at two levels (0 and 100 ppm), Si at two levels (0 and 1 g/L) on photosynthesis, gas exchange parameters, leaf relative moisture content, total protein, and anatomical indices were investigated. The results of this experiment showed that drought stress decreases relative leaf water content, total protein, photosynthesis, gas exchange parameters, and electrolyte leakage. Structurally, it caused a reduction in stomatal width, width of stomatal guard cells, stomatal density per unit area, and diameter of vascular tissues. Using SA and Si improved the photosynthesis, gas exchange parameters, relative moisture content, and total protein. In addition, the foliar application of SA and Si led to the improvement of the anatomical index caused by drought stress. The study results showed that drought stress had negative impacts on Scrophularia striata L, and using salicylic acid and silicon can improve drought stress tolerance in plants.

Seed priming is one of the ways to deal with stress conditions. The current research aims to improve the germination indices of indigo against oxidative stress caused by salinity through seed priming with pistachio wood vinegar in the form of a completely randomized basic design. Non-primed (control), hydro-primed, and primed seeds with concentrations of 300 and 200 times the dilution of pistachio wood vinegar were used in salinity conditions (0, 50, 100, and 150 mM NaCl). The results showed that salinity levels significantly decreased germination percentage, germination rate, germination rate coefficient, vigor index of seedling weight, fresh and dry weight of seedling, dry matter, radicle length, and anthocyanin content and increased the average germination time, the amount of total soluble sugars, reactive oxygen species, and malondialdehyde. Seed priming with pistachio wood vinegar significantly improved germination percentage, germination speed, and vigor index of seedling weight under saline conditions and reduced the average germination time. Seed priming with 300- and 200-times dilution of pistachio wood vinegar in normal conditions and 50 mM salinity improved the morphological characteristics of seedlings compared to unprimed seeds. In addition, seed priming with pistachio wood vinegar, 300 times dilution, under salinity conditions by 100 mM reduced the content of soluble sugars and malondialdehyde, improving the biochemical status of seedlings compared to oxidative stress. In general, it seems seed priming of indigo with pistachio wood vinegar diluted 300 times is more practical and economical as a modulating agent for the adverse effects caused by salt stress.

Haworthiopsis limifolia, a cactus native to South Africa, is one of the herbaceous ornamental plants belonging to the Asphodelaceae family. This succulent perennial plant is known for its medicinal properties, including antibacterial and antifungal properties. The production and cultivation of this plant are traditionally associated with low yield and time consumption, which do not meet any needs of the market, and the producer faces problems with mass production. To solve these problems, new propagation methods, such as tissue culture, are used. The objectives of this study were to introduce a novel protocol for disinfecting Hawthorn for in vitro tissue culture and investigate the effects of different levels of growth regulators, including BAP (benzyl amino purine) and IBA (indole butyric acid), on the micropropagation of this plant. The results showed that 1.5% sodium hypochlorite solution for 10 minutes was the best treatment for the disinfection of the isolated cultures. In addition, our results indicated that the highest number of succulents (10) belonged to the treatment of 1.5 mg /L BAP. According to the mean comparison, the best treatment for rooting was 1.5 mg/L of IBA.  The 1.5 mg/l concentration of BAP led to the maximum number of succulents. Moreover, BAP had a more significant effect than IBA on cacti's rooting, shooting, and suckering.

The destruction of the ozone layer leads to the penetration of some harmful solar radiation, such as ultraviolet rays into the atmosphere. These radiations have negative effects on plants’ growth and development. The current study investigated the effect of three UV radiation bands on plant growth, oxidative stress induction, and defense mechanisms in Melissa officinalis seedlings. The experiment was conducted in a hydroponics system under a completely randomized plan with three replicates. The seedlings, after a seven-leaf stage, were exposed to UV-A and UV-B for 20 min, and UV-C for three min daily for one week. The effect of different UV bonds was reported on oxidants, such as oxygen free radicals (ROS), hydrogen peroxide (H2O2), malondialdehyde (MDA), antioxidants (total antioxidants, phenolic compounds, anthocyanin and superoxide dismutase (SOD) enzyme activity), and seedling growth. The results revealed that UV-A radiation did not induce a significant effect on ROS, H2O2 and MDA contents compared with those of the control. However, under UV-B and UV-C ROS, H2O2 and MDA contents showed 59-89, 67-104, and 103-166 % increase compared with the control. All of the studied anti-oxidant content increased under three different UV radiations. The highest increase was reported for phenolic compounds with 148-178% compared with the control. The oxidant content increased under UV-B, and UV-C indicating that the plants’ anti-oxidant system was unable to sweep ROS and reduce the stress. Consequently, the radiation treatments reduced root and shoot fresh weight. Overall, the results indicated that the lemon balm plant was sensitive to UV radiation.

Plants need light for photosynthesis and respond to light through different photoreceptors. Apart from active photosynthetic rays (PAR), plants are also exposed to other rays including ultraviolet (UV) light. Ultraviolet rays are classified based on their wavelengths into UV-C (200-280 nm), UV-B (280-320 nm), and UV-A (320-390 nm). UV-C is the most dangerous range of ultraviolet light that is completely absorbed by the ozone layer. UV-B is very important because of its severe destructive effects on the growth and development of plants. UV-A radiation has less toxic effects than other wavelengths of ultraviolet radiation. Plants control growth and development changes in response to UV by creating a complex network of transcriptomes. Severe UV-B or UV-C stress leads to cell cycle arrest, chloroplast and mitochondrial dysfunction, DNA fragmentation, and finally programmed cell death (PCD). The amount of damage in plants varies depending on environmental factors, plant species, intensity of radiation, and type of radiation. Current knowledge about the eco-physiological impact of UV radiation on plants is limited. In this study, the effects of UV-A, UV-B, and UV-C on growth, induction of oxidative stress and resistance mechanisms of Melissa officinalis seedlings were studied. 

The seeds of Melissa officinalis were grown in containers with perlite. After germination, plants were transferred to pots containing washed perlite and irrigated with Hoagland's nutrient solution with one-fifth dilution. The lemon balm plants were exposed to ultraviolet rays (UV-A and UV-B for 20 minutes, and UV-C for 3 minutes) for one week after the 7-leaf stage. The control plants were exposed to visible light in the growth chamber. At the end of the treatments, growth parameters (fresh weight of shoots, roots, and leaves), oxidants (ROS, H2O2, and MDA), and antioxidants (total antioxidants, phenolic compounds, anthocyanins, and SOD enzyme activity) were measured. The experiment was conducted in a completely randomized design (CRD) with three replications (n=3). The analysis of variance (ANOVA) and SPSS 22 software were used for the statistical analysis of the data. Mean data were compared by Duncan's multiple range test (p ≤ 0.05). 

The results of the study revealed that there is a positive correlation of 0.9 (R2) between oxidant indices, such as ROS, H2O2, and MDA in the treated plants. The amount of oxidants in seedlings treated with UV-A did not show any significant difference in comparison with the control plants. UV-B and UV-C rays increased oxidant contents. UV-B and UV-C rays lead to the transfer of electrons to O2 and the formation of active oxygen species due to the photo-oxidation of the chloroplast membrane and mitochondria. The produced ROS are highly reactive and lead to oxidative damage to DNA, proteins, and lipid peroxidation. The antioxidant system in cells was able to remove ROS molecules.
The results of the analysis of variance obtained from the data showed that all the antioxidant indices measured in this study increased in all of the seedlings treated with UV. The increase of these organic compounds in plants was probably due to the induction effect of UV rays on the genes encoding the enzymes of relevant pathways. However, UV-B and UV-C rays led to an increase in the amount of ROS, increased lipid peroxidation, and ultimately cell damage, despite the increase in non-enzymatic and enzymatic antioxidant system components. This system was not able to control 100% of the effects caused by these rays in plants. Therefore, it led to the reduction of biomass in UV treatments, which was a general response in many plant species under severe stress conditions.

Considering the result of the present study, Melissa officinalis seedlings showed physiological changes when exposed to ultraviolet rays. Increasing the amount of antioxidants in UV treatments allowed plants to survive under oxidative stress conditions, but it still caused damage (e.g. oxidants increase and weight decrease) to the plant. Therefore, Melissa officinalis was sensitive to stress caused by ultraviolet rays.

Melatonin increases stress tolerance in plants. Saffron's red stigmas are the main Iran's industrial and export products. The aim of this study was to investigate the effect of melatonin on some morphophysiological and biochemical characteristics of saffron under drought-stress conditions. Drought stress was applied by polyethylene glycol 6000 at 10% and 20% levels. Root treatment of melatonin was applied at a concentration of 100 μM. Drought stress, particularly 20% stress, led to a decrease in growth parameters. Under 20% stress, the amount of chlorophyll a, chlorophyll b, carotenoids, and photosynthesis rate decreased by 22.32%, 35.84%, 51.35%, and 10.05%, respectively, while the ion leakage (2.70%), proline content (15.00%), and flavonoid (1.94%) increased. Exogenous application of melatonin has a positive effect on increasing plant resistance to drought stress by affecting physiological indicators such as photosynthetic parameters and the antioxidant system.

Drought is one of the limiting and effective abiotic factors in agricultural productivity in the world. Under drought stress conditions, plant growth factors decrease (Zhang et al., 2014; Brunner et al., 2015). Drought stress leads to the accumulation of reactive oxygen species in cells. Excessive accumulation of ROS causes lipid peroxidation and ion leakage. By inactivating enzymes, proteins, and nucleic acids, ROS reduces photosynthesis and the yield of crops (Altaf et al., 2022). Plants use different strategies to respond to stress. An increase in abscisic acid levels, compatible osmolyte content, protective enzyme activities, and antioxidant levels with inhibiting energy consumption pathways are among these strategies (Li et al., 2018). Natural or synthetic growth regulators such as melatonin can affect plant physiological processes at low concentrations. Melatonin regulates the biological responses of plants by modulating various physiological, biochemical, and molecular processes and finally increases the resistance of plants against drought conditions. Saffron with the common name Saffron and the scientific name Crocus sativus is from the Iridaceae family. As the most expensive agricultural and medicinal product in the world, saffron has a special place among Iran's industrial and export products (Farooq et al., 2009). Since most of the regions of Iran are facing the problem of water shortage, studying the responses of plants to water stress is of particular importance. The aim of this study was to investigate the potential improving effects of melatonin on the antioxidant and photosynthetic responses of Crocus sativus L. under drought-stress conditions. 

After disinfection, the corms were washed and transferred to pots containing perlite. Irrigation and addition of Hoagland's nutrient solution were done at one-week intervals. In order to apply drought stress, polyethylene glycol 6000 was used at two levels of 10% and 20%. Root treatment of melatonin with a concentration of 100 μM was done after applying drought stress. The fresh and dry weight of the samples, the relative water content, and the amount of photosynthetic pigments were measured according to the methods of Moradi Rikabad et al. (2019), Martı̀nez et al. (2004), and Arnon (1949), respectively. The maximum photosystem quantum efficiency (Fv/Fm) II was measured using a fluorometer apparatus (Pocket PEA) and the amount of net photosynthesis (Pn) was measured using a portable gas exchange device model CI-340. In order to measure proline content, ninhydrin was used as a reagent, and proline was used as a standard. The sugar in the samples was measured by the phenol-sulfuric acid method. The leakage of electrolytes was measured by the method of Lutts et al. (1996). The amount of H2O2 was calculated using the extinction coefficient of 0.28 mmol/cm. The measurement of phenolic and flavonoid compounds was done by colorimetric method using Folin-Ciocaltue reagent and aluminum chloride, respectively. The free radicals inhibition was measured by the DPPH method. This research was conducted as a factorial study in the form of a completely randomized design in three replications. To analyze the data, Minitab 16.0 was used, and the significance levels of differences between samples were determined using Tukey's test at the P ≤ 0.05 statistical level. Microsoft Office Excel 2013 was used to draw the graphs.

The results of the study showed that drought stress decreases the height, fresh and dry weight, and relative water content of the plant. Exogenous melatonin improves plant growth factors in these conditions. Melatonin probably stimulates plant growth factors by affecting plant metabolites and increasing the biosynthesis of phytohormones and facilitating the absorption of nutrients (Arnao, 2014; Naghizadeh et al., 2019). According to the results, drought stress causes a decrease in the content of photosynthetic pigments, Pn, and Fv/Fm. In fact, drought stress disrupts the balance between the absorption capacity and the use of light energy, causing disruption in photosynthesis, and damage to the photosynthetic apparatus (Pinheiro & Chaves, 2011). Exogenous melatonin treatment protects chlorophyll against abiotic stress by reducing lipid peroxidation and regulating the downstream genes of chlorophyll degradation (Yu et al., 2018). Exogenous treatment of melatonin by modulating the stomatal pore can also improve plant growth and increase Pn under drought stress (Liu et al., 2020). In this study, drought stress led to an increase in proline and soluble sugars, although these changes were not significant.
The Exogenous application of melatonin in these conditions decreased the content of these osmolytes. Under stressful conditions, the accumulation of compatible osmolytes improves turgor pressure, thereby preventing cell dehydration (Liang et al., 2018). The Exogenous application of melatonin may maintain the water balance in the plant through other ways and thus regulate the cell turgor pressure and reduce the content of compatible osmolytes (Ibrahim et al., 2020, Altaf et al., 2022). The results showed that drought stress leads to an increase in hydrogen peroxide content and ion leakage, although these changes were not significant, exogenous application of melatonin caused a decrease in hydrogen peroxide content and ion leakage while the content of phenol and flavonoid were increased. Drought stress often causes the accumulation of reactive oxygen species, which results in cell membrane damage. Under stressful conditions, melatonin can increase the activity of the H+-ATPase pump and contribute to the stability of the plasma membrane (Wang et al., 2019).

The results of this study showed that melatonin increases the resistance of Crocus sativus L. against drought stress by regulating the physiological and biochemical responses. In today's conditions, where water scarcity is one of the most important challenges in world agriculture, the use of new growth regulators, including melatonin, can be effective in increasing the tolerance of plants to drought stress and improving the growth and quality of agricultural products.